This invention relates generally to the production of cathode ray tubes (CRT) and particularly to an apparatus and method for aligning the envelope panel and electron gun mount assembly of such tubes.
During the initial stages in the production of a cathode ray tube, a phosphor screen is placed on the inside surface of a faceplate panel. A shadow mask, which serves as a color selection electrode, is then placed into the panel. The panel and a glass funnel which tapers into a neck, are then fitted together to form a completed envelope. An electron gun mount assembly is inserted into the neck and the envelope is evacuated and sealed.
During the operation of a color kinescope, the electron guns direct three electron beams toward the screen. The electron beams pass through the shadow mask at different angles so that each beam impacts a phosphor element of a different color emission resulting in the generation of a color visual display on the screen. Because the beams must approach the screen at the proper angles, it is necessary for the electron gun to be properly oriented with respect to longitudinal axis of the panel. Also, because the electron beams are scanned horizontally and vertically across the phosphor screen, the electron gun must be properly oriented with respect to the horizontal and vertical axes of the screen.
U.S. Pat. No. 4,189,814 discloses an apparatus for aligning the electron gun mount assembly and the neck of a CRT envelope. The apparatus described in this patent includes an upper support and a lower support which respectively support the CRT funnel and the electron gun mount assembly. In this apparatus, the alignment of the electron gun is accomplished using a pulsed laser and an optical system to rotate the electron gun to the desired orientation.
U.S. Pat. No. 3,807,006 discloses a CRT envelope alignment assembly in which three reference surfaces of the assembly engage three reference surfaces of the envelope to align the horizontal and vertical axes of the envelope panel with the assembly axes. This patent also discloses an assembly which aligns the longitudinal axis of the envelope with a vertical axis of the assembly. The assemblies disclosed in this patent function as desired for many tubes. However, difficulties frequently arise because the panels and funnels from which a completed envelope is formed vary in size within a range of tolerances. The reference surfaces are not capable of accommodating such variations.
The instant invention overcomes this difficulty by the provision of an apparatus and method for aligning the envelope panel and electron gun mount assembly of a CRT which accommodates for the size variations of the panels and funnels caused by the allowable tolerances of the components.